1. Field of the Invention
This invention relates to rolling mills producing hot rolled rod and bar products, and is concerned in particular with an improved and more efficient method of operating the finishing sections of such mills.
2. Description of the Prior Art
In a conventional rolling mill finishing section, a typical example of which is described in U.S. Pat. No. 3,336,781 and diagrammatically depicted at 10 in FIG. 3, roll stands S1-S10 are arranged in block form along the mill pass line PL. The work rolls of the successive roll stands define alternating oval and round roll passes “O”, “R”, with the axes of the successive roll pairs being staggered by 90° to thereby provide twist-free rolling.
Feed products FP1 are received from an upstream intermediate mill section (not shown) and are rolled into finished products FP2 in all or some of the successive roll passes S1-S10.
FIG. 4 is a rolling diagram depicting how the finishing section of FIG. 3 is typically employed to roll different sized finished products from feed products having the same or different entry sizes. For example, in one rolling sequence, all of the roll stands S1-S10 are employed to roll a feed product having a 17.1 mm diameter into a finished product having a 5.5 mm diameter. In another rolling sequence, the roll passes of roll stands S7-S10 have been rendered inoperative, for example, by replacing their work rolls with guides (a procedure commonly referred to as “dummying”). In addition, most if not all of the work rolls defining the roll passes of roll stands S1-S6 have been changed to thereby accommodate rolling of the same sized feed product into a finished product having a 9.0 mm diameter.
In still another rolling sequence, the roll passes of roll stands S5 and S6 are additionally dummied, with appropriate changes to the work rolls of the roll passes of roll stands S1-S4 in order to roll the same sized feed product into a finished product having a diameter of 11.5 mm.
It will be seen, therefore, that by progressively dummying roll passes, three different finished products sizes (5.5 mm, 9.0 mm, and 11.5 mm) are rolled from a feed product having the same entry size (17.1 mm). This rolling of different sized finished products from the same sized feed product is commonly referred to as “single family” rolling.
However, a problem with this conventional rolling methodology is that only a relatively narrow range of finished product sizes can be produced from one entry size. Thus, as shown in FIG. 4, four different entry sizes (17.1 mm, 18.5 mm, 19.5 mm, and 21.0 mm) are required to roll finished products ranging from 5.5 mm to 16.0 mm. When shifting from one entry size to another, in addition changing the rolls of some or all of the roll stands in the finishing section, changes also must by made to the rolls and guides of roll stands in upstream sections of the mill. This can take up to an hour, during which time the mill is inoperative and unproductive.
The primary objective of the present invention is to expand the range of sizes of finished products that can be rolled from the same sized feed product, thus advantageously reducing the number of differently sized feed products required to produce a given range of finished products.
A companion objective of the present invention is to broaden the range of finished product sizes that can be rolled from each feed product size.